1. Field of the Invention
The present invention relates to a droplet propelling device adapted for increasing and decreasing a pressure exerted on ink in an ink chamber to propel out a droplet of ink in the ink chamber through a nozzle communicating with the ink chamber.
2. Description of Related Arts
Inkjet printers have an inkjet head provided with a set of ink chambers each operable by exertion of a pressure to the ink chamber to propel out a droplet of ink in the ink chamber through a nozzle. The droplet of ink propelled out of the nozzle flies with a trailing tail, having a difference in speed developed between a head and the tail at the rear. There may be a droplet developed to have a leading core thereof accompanied by unnecessary fine droplet pieces (referred herein to as “satellites”). Satellites may adhere on a recording medium, degrading the print quality, or adhere on walls of a device, defacing the device.
As a technique to prevent such print quality degradation or device defacement, Patent Literature 1 (JP 2007-55147 A) has proposed using drive signals for driving an inkjet head, including therein paired pulse signals for swelling ink chambers. When driving the inkjet head, drive signals used each work, at a first pulse signal therein, to cause a variation in pressure of ink in an ink chamber, as necessary, to propel a droplet of ink out of the ink chamber, and at a second pulse signal therein, to cause a variation in pressure of ink in the ink chamber, in phase with the variation in pressure of ink caused by the first pulse signal.
When driving the inkjet head, each drive signal used can serve for an ink chamber to have a variation in pressure of ink caused by the second pulse signal, affording to amplify variations in reverberative pressures of ink in the ink chamber. This permits a droplet of ink separated from meniscus to be well defined, effectively preventing emission of satellites.
In recent years, there have been high-speeded inkjet printers, some of them needing propelling a droplet of ink onto a pixel on a recording medium, followed in a short time by consecutively propelling a subsequent droplet of ink onto a neighboring pixel in a transfer direction of the recording medium. There have been also inkjet printers employing a multi-droplet system for consecutively propelling an increased or decreased number of ink droplets onto a single pixel to provide a gradation, needing two or more droplets of ink to be propelled onto the single pixel in a consecutive manner at short intervals of time.
To cope with such the need for ink droplets to be consecutively propelled out, essential is how to quickly arrange a situation that permits a second or any subsequent droplet of ink to be consecutively propelled out with an adequate pressure. Upon such a consecutive propelling of ink droplets, the ink chamber is to have controlled pressures, whereon Patent Literature 2 (JP2002-127418 A) has proposed propelling out a respective droplet of ink, suppressing residual vibrations in the ink chamber. However, as a measure to suppress residual vibrations, there has been proposed no more than controlling ink in the ink chamber to a static pressure, failing to implement quickly propelling out a subsequent droplet of ink with an adequate pressure.
Further, there are inkjet printers operable under low temperature environments, where the viscosity of ink is increased. To this point, for a desirable amount of ink to be discharged, if the inkjet head is driven with increased voltages, it has droplets of ink propelled through nozzles with longer tails. Long tails tend to go disrupt, the longer the more in number of disrupt droplet pieces, with increased tendencies to emit satellites.
Satellites may adhere on a recording medium, degrading the print quality, or adhere on walls of a device, defacing the device. To this point, Patent Literature 3 (JP2000-255055 A) has disclosed proceeding without making any record under low temperature environments having tendencies to emit satellites, to enter a warm-up operation for heating an inkjet head, before starting a record.
However, in such inkjet recording devices under low temperature environments having tendencies to emit satellites, there is a warm-up operation entered before starting a record, thus taking a long time to record an image.